The disclosure relates to a drying mill for coarse-grained or fine-grained material, especially also suitable for calcining gypsum, with a housing in which a feed device for a propelling gas, which leads to a lower region, and a comminuting device, are arranged one above the other.
Mills with drying function are especially used in plants for calcining gypsum. The raw material must be comminuted before burning. A calcining plant, therefore, has a grinding device as the essential component. That applies especially in the case of processing recycled gypsum, like REA gypsum, as source material.
Drying mills, which are based on a ball and ring mill, are known from prior public use. They are marketed for example by Claudius Peters Technologies under the designation EM mill. It has a grinding device which comprises a plurality of large grinding balls which run on a grinding track. During operation, the ground material is discharged outwards, and gathered and dried there by a rising propelling gas until it reaches a sifter which is arranged vertically above the grinding device. Oversized particles cannot be transported upwards by the propelling gas stream, but fall back onto the grinding track. The material which reaches the sifter is separated into a fine fraction and a coarse fraction, wherein the coarse fraction is guided back into the grinding device via guides. The fine fraction is separated out and discharged from the mill. These mills certainly deliver very good results and are extremely stable, but are not suitable for processing all raw materials. Such materials, which can be comminuted better by breaking up than by crushing, as when grinding, can cause difficulties. Also, the energy expenditure for driving the heavy grinding gear is rather high.
For processing such materials, with which comminuting is essentially defined by a disintegrating of agglomerations, another type of construction has been known. In this case, such a type of construction concerns a hammer mill. It is marketed for example under the designation Delta Mill by Claudius Peters Technologies. It has a hammer grinding gear and a sifter gear which is arranged next to it on the same drive shaft. The material which is fed from one side to the hammer grinding gear is ground, and further transported by a propelling gas stream into the sifter gear. The sifter gear comprises paddles which reject oversized particles and transfer only fine particles to an outlet. Such hammer mills are certainly suitable for processing material which is not to be processed, or processed only with difficulty, by the ball and ring mill, but also have disadvantages. Hammer mills are sensitive to foreign bodies, and they are susceptible to wear on account of the movable hammer elements. Furthermore, they take up a comparatively large amount of room on account of the horizontal position of the drive axis for the hammer grinding gear.
Starting from the first-named type of construction, an object is to create a mill with drying function, which with high stability is less costly, and also to provide a corresponding operating method.